Telephone companies are deploying a variety of new digital technologies to upgrade their networks and provide a wider range of communication services. Digital networks require protocol analysis and other testing to monitor performance and facilitate maintenance operations. In a typical installation, a protocol analyzer or other digital test device connects to a facilities access die (FAD) group type maintenance port on the digital switch. For test purposes, the switch breaks an identified communication link and routes the communications through the FAD port. Effectively, the test device is serially connected into the digital circuit under test. The test device passively monitors and analyzes the communication signals and passes the signals back through the port for routing to the appropriate destination without the subscriber's knowledge.
An exemplary test system known in the art comprises the Hekimian React Model 2001 system implemented with other pieces of equipment as shown in FIG. 1. The React Model 2001 test control 101 is an operational support device having a graphical user interface (GUI) for testing the integrity of advanced data packet services. The devices can operate as either protocol analyzers or synchronous optical network (SONET) test devices. The test device is hooked up via the FAD group type maintenance port 103 to a digital cross-connect system 102 locally. In other words, the test device 104 is mounted near the digital cross-connect system 102, and a pair of T1 circuits connect the FAD port of the digital cross-connect system 102 to the test device 104.
The test control 101 controls mapping in the digital cross-connect system 102 through X.25 administrative port 105. When operations personnel want to test a T1 circuit that runs through the digital cross-connect system 102, a technician inputs a request into the test control 101. The test control 101 sends commands to the digital cross-connect system 102 to map the T1 circuit through the FAD port channels, i.e., to break the physical connection and make the T1 channel available at the facilities access die group maintenance port 103. The test die group 103 then feeds the circuit to be tested into the test device 104 where it passively runs through the test device 104 and then returns to the digital cross-connect system 102. All types of protocol analysis or other testing can be performed by test device 104. The test device 104 reports its test results to test control 101. When the testing is done, the circuit is remapped back to go from one of the input ports 106.sub.1 to 106.sub.m to one of the output ports 107.sub.1 to 107.sub.n of digital cross-connect system 102.
The testing system shown in FIG. 1 gives the network operations personnel the ability to test some of the fast packet services such as frame relay, SMDS, etc., as they are developed and included in the network. This requires adding test elements out in the field, such as in each central office of a public switched telephone network having the digital services capability. The system has the disadvantage that the test elements are only occasionally used for testing and hence are underutilized. Furthermore, if a test element becomes defective, then there is essentially no way to test circuits in that office. The maintenance of the testing system is then compromised.
Installation of such elements in many switching offices as shown in FIG. 1 can also become quite expensive as the network grows in a large service area. For example, wherever a fast data packet service is deployed in a switching office that has an SMDS switch, pieces of equipment, such as a Hekimian base model 6700 test unit with appropriate test cards and accesses, must be installed and coupled to the FAD port of each digital switch as well in order to accommodate the test system and test the service. This forces the network operator to incur the large expense of purchasing, installing and maintaining a large number of the test devices. Upgrading also is expensive because the operator must replace software in each test device or replace all of the test devices with improved models.
Even in systems with remote testing of digital communication links, a test device is required at the location of the circuit under test. For example, U.S. Pat. No. 4,998,240 issued to Williams on Mar. 5, 1991 discusses a system for remote testing of ISDN lines. A standard U-interface bus in the central office supplies D-channel data from the ISDN line to a personal computer at a central office which performs protocol analysis of the data. A second computer at a remote test facility communicates with the analyzer via a dial-up line. U.S. Pat. No. 5,260,970 issued to Henry et al. on Nov. 9, 1993 similarly discusses an ISDN protocol analyzer for insertion in a U-interface data stream between a central office and customer equipment. For other examples of testing systems using test devices at the location under test, see also U.S. Pat. Nos. 5,434,845, 5,276,529, 5,195,124 and 4,870,638.
U.S. Pat. No. 5,457,729 issued to Hamann et al. on Oct. 10, 1995 uses interoffice T1 trunks to provide remote access to links under test. However, the trunks connect an integrated digital service terminal (IDST) including relays to break an SS7 link under test. A digital protocol analyzer is coupled in series in the link in order to provide for coupling of the T1 trunk to the link and testing of the link.
U.S. Pat. No. 5,375,159 issued to Williams on Dec. 20, 1994 discusses a protocol analyzer for common channel signal links. The analyzer tests switch functions remotely via SS7 digital communication links. The protocol analyzer is located at a signal transfer point and is switchably connected to SS7 digital communication links between the STP and a plurality of central offices via a port selector. The port selector provides a switched selection of a particular central office under test and connects the protocol analyzer through the two ports coupled to the links to the particular central office to facilitate testing of that central office. The test capability of the system is limited to the interoffice SS7 signaling functionality of the central offices. The protocol analyzer apparently can not test the actual normal line side or trunk side communication links or facilities. Also, the links from each switching office to the central location are dedicated to the individual switching office and cannot readily be reallocated to other offices.
These known testing systems and procedures have various drawbacks. In particular, a test device has to be located at each one of the locations at which circuits are to be tested or connect to the switch at each location via dedicated facilities. Consequently, a large number of test devices are necessary to provide comprehensive testing ability for a large communications network. This in turn makes it more difficult and more expensive to implement, maintain and progressively upgrade testing of advanced communications services as those services are introduced and expanded in a network.